The present invention relates generally to detection of deformed leads of semiconductor devices. More particularly, the invention is concerned with a method and an apparatus for detecting vertical and/or horizontal deformation (such as misorientation, abnormal bending, floating or the like, i.e. irregular states) of leads of a semiconductor device.
Heretofore, in implementation of various electronic circuits, there has widely been adopted such a device structure in which a printed wiring substrate is used for mounting thereon a semiconductor device. At present, this kind of electronic device is generally manufactured by using an automated manufacturing or mounting apparatus.
In conjunction with the automated manufacturing of the electronic devices, it is noted that the presence of deformed leads in a semiconductor device to be mounted on a printed wiring substrate provides an obstacle to realization of correct connections between the leads of the semiconductor device and the wiring patterns printed on the substrate. As typical ones of such deformation of the leads, there may be mentioned vertical deformation (i.e. deformation in the direction in which the leads extend, such as rowwise misorientation), horizontal deformation (i.e. deformation in the direction in which the semiconductor device extends, such as abnormal bending) and the like irregularities. In order to evade such obstacles, it is necessary to inspect in advance the leads of a semiconductor device for the presence of the abovementioned deformations so that only semiconductor devices having lead wires attached in the correct state are allowed to be positioned or placed on the printed wiring substrate.
Before entering into a description of the inspection or detection of such deformations or irregularities of the leads of a semiconductor device, elucidation will be made in detail of the vertical and the horizontal deformations of the leads by reference to FIGS. 1 and 2 of the accompanying drawings, in which FIG. 1 is a top plan view of a typical flat package IC device and FIG. 2 is a side elevational view of the same. In these figures, a reference numeral 2 denotes generally lead wires or leads for short, wherein leads suffering from the vertical deformation are designated by reference symbols 2a and 2b while those undergone the horizontal deformation are designated by reference symbols 2c and 2d, respectively. As mentioned above, the phrase "vertical deformation" is contemplated to mean misorientation of the leads in the rowwise or columnwise direction in which the individual leads are to extend in an orderly orientation, while the phrase "horizontal deformation" is used to mean deformation of the lead in the direction orthogonal to the rowwise or columnwise direction such as irregular or abnormal bending of the leads. The former deformation may also be referred to as misoriented deformation with the latter being termed bending deformation.
Now, in accompanying the trend of higher density implementation of the semiconductor device and miniaturization thereof, the lead wires of a semiconductor device tend to increase in the number with the inter-lead space (lead pitch, to say in another way) being more and more decreased. Under the circumstances, the vertical and horizontal deformations of the lead wires may frequently bring about formation of short-circuits between adjacent electrodes on the printed wiring substrate or render it impossible or at least extremely difficult to solder correctly the leads to the electrodes formed on the printed substrate upon mounting of the semiconductor device, which ultimately results in failure of contact or connection, thus giving rise to a serious problem in respect to the reliability of the connection.
As an attempt to overcome the problems mentioned above, there have already been proposed methods of detecting the vertical and horizontal deformations of the leads of semiconductor devices, typical ones of which are disclosed in JP-A-63-5243 and JP-A-62-79644 and shown in FIGS. 3 and 4 of the accompanying drawings, respectively.
In FIG. 3, a reference numeral 3 denotes a semiconductor device, 4 denotes a head for holding the semiconductor device 3, and a numeral 5 denotes an image pick-up device such as a camera used for detecting the deformations of leads 6 of the semiconductor device 3.
The principle underlying the lead deformation detection method shown in FIG. 3 resides in that one-dimensional pattern data representing an image of the lead array along a line in a plane transversal thereto is obtained from the output of the camera 5 which is positioned to pick up light rays reflected from the semiconductor device and the leads under inspection. The pitch of the density patterns (dark and bright patterns) which appears in the one-dimensional pattern data in dependence on the intensities or quantities of the picked-up light rays is determined for thereby detecting the deformations of the leads on the basis of variations in the pitch.
On the other hand, in FIG. 4, a reference numeral 7 denotes a semiconductor device, 8 denotes a light projector for illuminating the leads of a semiconductor device under inspection with a light beam, 9 denotes a one-dimensional position detector and 10 denotes the leads.
The principle of the lead deformation detecting method illustrated in FIG. 4 is seen in that reflected light pulses resulting from illumination of the leads 10 with the light beam are received by the detector 9, wherein the deformations of the leads of the semiconductor device are determined on the basis of the inter-pulse interval and the intensities or quantities of the reflected light pulses.
In the case of the deformation detecting method illustrated in FIG. 3, the horizontal deformation (2c in FIG. 2) is detected on the basis of difference in the length among the projecting leads. Consequently, intrinsic variance in the length of the leads 6 affects the result of measurement, making it difficult to detect the horizontal deformation with a high accuracy.
On the other hand, in the case of the deformation detecting method shown in FIG. 4, detection is susceptible to the influence of the surface states of the lead wires because the detection is based on the quantities of light reflected from the leads, thus giving rise to a problem in respect to the reliability and consistency of the results of detection. Besides, in order to detect the vertical and the horizontal deformations of all the leads, it is necessary to move the light beam projector 8 together with the one-dimensional position detector 9 for scanning the leads with the light beam or alternatively to move the semiconductor device 7, which means that the time involved in the inspection will intolerably be increased. Besides, inaccuracy, if any, in the scanning or positioning of the light beam projector 8 and the detector 9 affects adversely the detection of the vertical and the horizontal deformations of the leads, to another disadvantage.